What is it? Who uses it? What types of ventilators?

What types of interfaces? and more.

You or your child may have been diagnosed with a disease or condition that affects breathing, or you or your child may be recovering from an operation and need help breathing for a while. Your physician has informed you that a mechanical ventilator will help you or your child breathe. This is a brief explanation of mechanical ventilation and an introduction to ventilator-assisted living – what it means for one's health and lifestyle.

What is ventilation?

Ventilation is the process by which the exchange of oxygen (O2) and carbon dioxide (CO2) occurs in the alveoli in the lungs. The alveoli are small air sacs at the end of the bronchial tree in the lungs, and it is through the walls of these air sacs that O2 diffuses into the blood and CO2 diffuses out of the blood. Ventilation is a constant process of maintaining the proper balance between the two.

What is mechanical ventilation (MV), also known as assisted ventilation?

Breathing can be assisted mechanically for people who have spontaneous but weak breathing or for people who cannot breathe on their own. Mechanical ventilation (MV), or assisted ventilation, can be used on a short-term or long-term basis, depending on the individual's medical needs.

Short-term use of MV generally occurs in a hospital ICU, e.g., during an acute illness or during and after an operation, until an individual can breathe unassisted. In the ICU, MV can be delivered noninvasively through a face or nasal mask, but is usually delivered by an endotracheal tube placed in the mouth and down the throat (intubation).

In some cases, short-term use of MV in the hospital turns into longer-term use. Generally, if an individual has been intubated for an extended period, such as two weeks, a tracheotomy is performed. This is a surgical procedure that creates an opening in the neck to the windpipe. A plastic or metal tracheostomy tube is placed into the windpipe through this opening. The individual relies on air delivered by a machine through the tracheostomy tube rather than through a tube inserted into the nose or mouth and into the windpipe. When the person becomes medically stable, but still needs to use tracheostomy ventilation, he or she is usually discharged from the hospital to a skilled nursing facility or to home care if feasible. Eventually, the individual may be able to breathe unassisted or to be converted to noninvasive ventilation.

Long-term MV may be necessary for extended periods or for life. It may be indicated for some people with stable/chronic conditions such as neuromuscular disease, obstructive lung disease or other conditions that limit the use of the breathing muscles and/or involve the airways.

What are the benefits of using MV?

There are several interrelated benefits that include:

maintaining and/or improving the oxygen/carbon dioxide levels in the blood;

resting the respiratory muscles;

decreasing the work of breathing;

inflating the lungs more fully;

improving cough by stacking breaths;

improving sleep quality and breathing during sleep;

preventing/avoiding hospitalization for respiratory complications;

improving quality of life, and;

improving survival.

Who uses long-term MV?

Infants, children and adults who have neuromuscular and/or musculoskeletal diseases and conditions that affect the respiratory muscles, spine and ribs may have reduced lung capacity and/or stiff chests. Their lungs are healthy but they need MV to help augment or take over the work of the respiratory muscles, primarily the diaphragm, during inspiration (breathing in). Some individuals may be able to breathe on their own for most of the day and need to use MV only during the night; others may require 24-hour MV. The diseases and conditions include but are not limited to post-polio; amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease; muscular dystrophy; spinal muscular atrophy (SMA) and scoliosis/kyphoscoliosis.

People who have sustained a high spinal cord injury often need MV if the spinal cord has been injured at or about the fourth cervical vertebra (C4) or higher, and the respiratory muscles are paralyzed. After rehabilitation and special breathing exercises, some individuals are able to breathe on their own for short periods, but, generally, they must use a ventilator for the rest of their lives.

Some people with high spinal cord injuries choose diaphragmatic or phrenic pacing to assist their breathing. This involves an operation to implant electrodes on the phrenic nerves connected to wire leads implanted subcutaneously (under the skin). An external transmitter activates the leads to deliver stimulating pulses to the phrenic nerves, causing the diaphragm to contract. Thus, no ventilator is needed, although many keep the tracheostomy open for suctioning.

Adults with sleep-disordered breathing syndromes such as obesity hypoventilation (underventilation) or infants and children with con-genital central hypoventilation syndrome (CCHS) need to use MV only during the night. Children with CCHS may also be good candidates for diaphragmatic pacing.

There are some people who have severe exacerbations of chronic obstructive pulmonary disease (COPD), such as emphysema or chronic bronchitis, or severe cardiopulmonary conditions such as congestive heart failure or cor pulmonale, whose breathing is helped by MV.

Some individuals who have had tuberculosis can also benefit from using MV.

What is a ventilator?

A ventilator is the equipment used to mechanically assist breathing by delivering air to the lungs. Many people may be familiar with ventilators in the hospital setting, such as the ICU, where large complex acute care ventilators are used. The ventilators used in the home are small, lightweight and portable; they can be mounted on wheelchairs or carts or put on a bedside stand. Most of these operate on household electric current. Many have internal batteries, can be operated with external batteries, and newer models features “hot swappable” batteries, extending the time a ventilator user can be away home. It is advisable to have a backup battery or even a generator readily available in case of power outages or emergencies.

How does MV work?

The diaphragm is the primary muscle for inspiration, along with the intercostal muscles between the ribs. Other muscles of the chest, neck and shoulders play smaller roles. When these breathing muscles are weakened or paralyzed, breathing becomes difficult or impossible.

A mechanical ventilator can take over the act of breathing completely or make breathing easier by assisting weakened respiratory muscles.

The muscles of the abdomen are important for breathing out (expiration) and for an effective cough. Weak expiratory muscles result in impaired cough and inability to clear secretions that can lead to respiratory infections and pneumonias. In certain neuromuscular diseases, the bulbar muscles – those responsible for swallowing, speech and coughing – can become progressively impaired. Cough can be assisted with the use of manual and/or mechanical methods. There are several cough assists device available, e.g., Comfort Cough™ (Seoil Pacific Group); CoughAssist E70, CoughAssist T70 (Philips Respironics); Mini Pegaso A-Cough, Mini Pegaso A-Cough Perc, Pegaso Cough, Pegaso A-Cough Perc (Dima Italia S.r.l.); Nippy Clearway (B & D Electromedical); Pulsar (Siare Engineering International Group S.r.l.); The Vital Cough™ System (Hill-Rom).

How did mechanical ventilation develop?

The iron lung or "tank" was the first effective form of mechanical ventilation and one of the earliest iron lungs, often used to resuscitate drowning victims, dates from 1838. A century later, in the 1930s, improvements in the iron lung made widespread use of mechanical ventilation possible. Iron lungs are an example of negative pressure ventilators. Other forms of negative pressure ventilation include the chest shell or cuirass, Nu-Mo suit and Pulmo-wrap.

Positive pressure ventilators developed as a more effective breathing option than the larger, bulkier negative pressure devices. Since the 1980s, computer technology has enabled manufacturers to produce even smaller, lightweight ventilators that are easier to transport and operate, and are better suited for people living at home.

What is negative pressure ventilation?

When the pressure around the chest is negative – lower than atmospheric pressure – the chest expands to allow air to enter the nose and mouth. Iron lungs enclose the whole body, except for the head, and create pressure changes between the chest and the encasing shell of the unit. Other forms of negative pressure ventilation, also known as body ventilators, include the chest shell or cuirass, Nu-Mo suit and Pulmo-wrap. The Porta-Lung™is a small and more mobile version of the iron lung. Today, some people still use an iron lung, chest shell or Porta-Lung™.

All negative pressure ventilation systems provide MV noninvasively to the body – no surgical operation, such as a tracheotomy, is necessary.

What is positive pressure ventilation?

Positive pressure – higher than atmospheric pressure – pushes air into the lungs. It can be administered either noninvasively via a wide variety of nasal, facial and oral masks, nasal pillows (small cushions that fit into the nostrils), and mouthpieces – with tubing attaching to the ventilator or invasively via tracheostomy.

Positive pressure ventilators were developed as a more effective breathing option instead of the larger, bulkier negative pressure devices.

The high flow of air from positive pressure may cause dryness in the nasal passages and upper airway, and humidifiers may help relieve symptoms of nasal stuffiness, dry mouth and thick nasal secretions.

An integrated humidifier is a feature of some of the ventilators.

What is noninvasive positive pressure MV?

In noninvasive positive pressure MV, tubing connects the ventilator to the person via an interface. Interfaces include a wide range of nasal, oral or facial masks, nasal pillows (small cushions that fit into the nostrils), and mouthpieces, lipseals or other oral appliances. The nasal and facial masks can be custom-made.

The advantages of noninvasive MV: avoids the need to create an opening in the neck (tracheotomy) that may become a site for infection and irritation, permits normal speech and swallowing (if unaffected by the neuromuscular disease), preserves sense of taste and smell, and reduces need for attendant/personal assistance, family caregivers or nursing care related to MV.

Disadvantages include having the mouth and/or nose covered by the interface, possible upper airway obstruction, inability/claustrophobia in tolerating the mask, and safety issues if 24-hour MV is needed. Noninvasive MV may not be successful, or no longer work, when secretions are heavy and when there is progressive impairment of the muscles responsible for swallowing, speech and coughing, i.e., the bulbar muscles.